Dynamic random access memory (DRAM) circuits are widely used in graphic and processor applications for storing data. The DRAM circuit includes a number of memory cells, and each cell has a capacitor and a transfer transistor. The capacitor stores binary data, while the transfer transistor retains the charge. In the read cycle, the transfer transistor interrogates the cells through bit lines. A field effect transistor is commonly used as the transfer transistor. The capacitor generally includes two electrodes separated by a barrier, for example, insulating material, to provide isolation.
Memory cells are likely to appear in two types, which include a deep trench (DT) capacitor formed in the substrate under the transfer transistors and a cell having a stacked capacitor that is built over and between transfer transistors. The physical size of electronic devices is ever reducing, and, as a result, the number of memory cells on a DRAM chip has increased dramatically in a short period. In the case of DT capacitor, the deep trench is made smaller to conserve space on the substrate for other components. The downsizing can lead to a significant reduction in the perimeter of the deep trench, and the electrical charge capability of the capacitor is strongly associated with the surface area.